The Astronomical Journal
The nebula J222557+601148, tentatively identified by Morris et al. as a young Galactic supernova remnant (SNR) from Spitzer Galactic First Look Survey images and a follow-up mid-infrared spectrum, is unlikely to be an SNR remnant based on Hα, [O III], [S II] images, and low-dispersion optical spectra. The object is seen in Hα and [O III] λ5007 images as a faint, roughly circular ring nebula with dimensions matching that seen in 24 μm Spitzer images. Low-dispersion optical spectra show it to have narrow Hα and [N II] λλ6548,6583 line emissions with no evidence of broad or high-velocity (v ≥ 300 km s–1) line emissions. The absence of any high-velocity optical features, the presence of relatively strong [N II] emissions, the lack of detected [S II] emission which would indicate the presence of shock-heated gas, plus no coincident X-ray or nonthermal radio emissions indicate that the nebula is unlikely to be an SNR, young or old. Instead, it is likely a faint, high-excitation planetary nebula (PN) as its elliptical morphology would suggest, lying at a distance ~2-3 kpc with unusual but not extraordinary mid-IR colors and spectra. We have identified an m r' = 22.4 ± 0.2 star as a PN central star candidate.
Fesen, Robert A. and Milisavljevic, Dan, "The Nature of the Strong 24 Μmspitzersource J222557+601148: Not a Young Galactic Supernova Remnant" (2010). Open Dartmouth: Faculty Open Access Articles. 3435.